1. Field of the Invention
The present invention generally relates to lightwave communications systems and, more particularly, to a method and apparatus for controlling the power level of an optical signal.
2. Description of the Related Art
Retinal and other types of eye injury can occur from inadvertent direct exposure to the optical signals used in present lightwave communication systems. The power and wavelength of optical signals used in such systems presents an exposure danger. Generally, these systems operate with signals having relatively high power concentrated in a tiny beam located outside the visible spectrum region of light.
Recent developments in optical networking have only heightened existing safety concerns. For example, optical amplifiers and other optical components are now being developed to drive optical signals to even higher output power levels. Mutli-wavelength systems, such as dense wavelength division multiplexed (DWDM) systems, are also a concern because the total optical power in the optical fiber is the sum of the powers of the individual wavelength components. Consequently, optical systems having total output power of 27 dBm or more are now being realized as a result of advances in optical amplifier and multi-wavelength optical networking technologies.
Because the extent of injury is most likely proportional to the total output power and the time of exposure, it is necessary to quickly shut off or reduce the output power of a network element in the event of a fiber cut, removed connector, or any other discontinuity in the optical fiber path. In prior arrangements, control of upstream network elements relies entirely upon downstream network elements. For example, downstream network elements perform fault detection and localization by monitoring the degradation or interruption of the forward propagating optical signal (i.e., the signal propagating downstream). If such a degradation or interruption is detected, the downstream network element must notify the upstream network element of the fault. This scheme is limited in that handshaking between two network elements is necessary, which slows the response of the system. Present safety standards require faster shutdown times as the optical power levels are increased. In addition, if the downstream network element cannot communicate with the upstream network element (e.g., there is a discontinuity in the optical path), then this scheme will fail to switch off the upstream network element.